Substrate having uniform tungsten silicide film and method of manufacture

ABSTRACT

A tungsten silicide film is deposited on a substrate from a premixed deposition gas mixture comprising: (i) silicon source gas, such as SiCl 2  H 2  and (ii) tungsten source gas, such as WF 6 . A seeding gas, such as silane, is used during the initial deposition stages to deposit a substantially uniform interfacial WSi x  layer on the substrate, so that the tungsten to silicon ratio of the WSi x  layer is substantially uniform through the thickness of the WSi x  film. An apparatus for performing the process is also described.

CROSS-REFERENCE

This is a continuation of application Ser. No. 08/480,652, filed on Jun.7, 1995, now abandoned, which is a Continuation-in-part of U.S. patentapplication Ser. No. 08/064,328, filed May 18, 1991, now U.S. Pat. No.5,500,249; which is a Continuation-in-Part of U.S. patent applicationSer. No. 07/995,211, filed on Dec. 22, 1992, now abn., and aContinuation-in-Part of Japanese Patent Application Serial No. 5-76894,filed on Apr. 2, 1993.

BACKGROUND

This invention relates to the deposition of tungsten-silicide (WSi_(x))films.

Refractory metal silicide films, such as tungsten silicide, are used inthe manufacture of semiconductor integrated circuits such as schottkybarriers, ohmic contacts and gate metallizations. Traditionally,polysilicon layers were used for these semiconductor circuits. However,advances in integrated circuit technology led to a scaling down ofdevice dimensions, and an increase in chip size and complexity. Highercomplexity chips such as VLSI's (very large-scale integrated circuits),require closely spaced inter-connection lines with smallercross-sectional areas than conventional integrated circuits. The smallcross-sectional area of the interconnection lines results in generationof more resistive heat. Close spacing results in less heat dissipation.This combination of more resistive heat generation and less heatdissipation can cause high temperatures which can result in partfailure. Also, the higher resistivity increases the RC time constantwhich affects the delay time of the circuit. Low delay times aredesirable for high speed circuits.

To overcome this problem, refractory metal silicides films having lowerresistivities than polysilicon films were developed for use in theseimproved integrated circuits to obtain lower delay times and so thatless heat is generated within the circuit. For gate metallizations, alow resistivity tungsten silicide film is deposited on top of a layer ofpolycrystalline silicon (polysilicon), to form a layered structurecalled a "polycide" structure.

At first, tungsten silicide films were deposited by physical vapordeposition techniques such as sputtering and electron-beam evaporation.However, these techniques gave films with poor conformal coverage overthe steps and trenches of the polysilicon layer and non-uniformstoichiometry. Alternative deposition techniques such as low pressurechemical vapor deposition (LPCVD) were developed, and provided metallicsilicide films with superior conformal coverage and superior properties.

Initially LPCVD processes for the deposition of tungsten silicide(Wsi_(x)) films were based on the reduction of tungsten hexa-fluoride(WF₆) by monosilane (SiH₄). However, WSi_(x) films produced usingmonosilane contained high levels of fluorine (often greater than 10²⁰fluorine atoms/cc). The high levels of fluorine led to degradation ofthese films due to migration of the fluorine atoms at operatingtemperatures. In addition, these films suffered from lower step-coverageand post-annealing problems which can lead to cracking and delaminationof the tungsten-silicide layer.

Problems created by the silane chemistry can be avoided by usingdichlorosilane (DCS), SiH₂ Cl₂, instead of monosilane. Tungsten-silicidefilms produced from the reduction of WF₆ by DCS exhibit lower fluorinecontent, improved step coverage and stronger adhesion.

However, in spite of these encouraging results, the DCS/WF₆ process hasnot been extensively adopted by the semiconductor industry because thereare additional problems with these technologies.

First, these processes can fail to produce WSi_(x) films with a uniformtungsten to silicon ratio through the thickness of the film. In thestrata deposited in the initial stages of deposition (which laterbecomes the "interfacial layer" between the WSi_(x) film being depositedand the substrate), the films deposited from current methods generallyexhibit a value of "x" that is below the optimal range of 2.0 to 2.8.This phenomena is especially true for WSi_(x) layers deposited onpolysilicon. Values of x smaller than 2 (x=2 corresponds to thestoichiometry of the stable tungsten silicide, WSi₂) in this interfacialstrata are undesirable. The formation of an interfacial tungsten-richstrata can result in delamination of the WSi_(x) layer during annealingof the fully processed wafer in the final stages of processing. Voidscreated by the migration of Si ions from the Si rich polysilicon layerto the Si deficient WSi_(x) layer can also lead to poorer performance.

It is difficult to non-destructively detect formation of thetungsten-rich layer during the initial steps in the process offabricating the integrated circuit chip. It is only in the final stagesof the manufacturing process, when the fully processed wafers are worthbetween $50,000 to $100,000 each, that the delamination is discovered,and the entire wafer must be scrapped. This expense limits the use ofcurrent DCS/WF₆ processes on an industrial scale.

Another problem with conventional CVD processes is that it is difficultto deposit a tungsten silicide film having a uniform sheet resistance.Typically, as a silicon content of the film is increased, the tungstensilicide film has a higher sheet resistance, and a greaternon-uniformity in sheet resistance. Conventional tungsten silicide filmshave sheet resistances from about 500 to about 1500 μΩ-cm, and moretypically from about 600 to about 1200 μΩ-cm. As the composition of thefilm is tailored to produce the higher sheet resistance, namely above1000 μΩ-cm, the non-uniformity of the sheet resistance of the film alsoincreases. Conventional CVD methods typically deposit WSi_(x) filmshaving sheet resistances with non-uniformities of about 1.5 to about2.5%.

Another problem associated with use of current DCS/WF₆ processes arisesfrom the nucleation of silicon containing particles in thedichlorosilane gas phase. These particles accumulate and deposit on thewalls of the deposition chamber. These deposits eventually fragment andgenerate particles which contaminate the wafer.

LPCVD equipment is typically sophisticated and expensive. Thus, newprocesses requiring substantial modification to existing equipment areavoided due to the high costs associated with such modifications.Accordingly, processes that can be implemented on conventional CVDequipment are highly desirable.

Therefore, there is a need for WSi_(x) films having substantiallyuniform tungsten to silicon ratios through the thickness of the film andhaving low concentrations of fluorine. There is also a need for methodsto deposit such films, and it is also desirable to be able to useconventional CVD equipment to deposit such films. There is also a needfor a CVD process capable of depositing WSi_(x) films having uniformsheet resistance, particularly at higher sheet resistivities.

SUMMARY

The present invention provides a WSi_(x) film and methods for theirmanufacture that satisfy the above needs. The WSi_(x) films prepared inaccordance with the present invention have a high degree of uniformitythrough the thickness of the film, a low concentration of fluorine andother impurities within the film, and can be deposited usingconventional CVD equipment.

The present invention is directed to a WSi_(x) layer on a substrate,where the value of x in the layer is substantially uniform through thethickness of the WSi_(x) layer, and the WSi_(x) layer contains less than10¹⁸ fluorine atoms/cc, and more preferably less than 10¹⁷ fluorineatoms/cc. The layer of WSi_(x) is at least 300Å thick. By "substantiallyuniform" it is meant that the average value of x within each strata ofthe WSi_(x) layer is between ±10% of the average bulk value of x throughthe thickness of the WSi_(x) layer. Typically, the bulk value of x isfrom about 2.0 to about 2.8, and preferably the value of x is from about2.2 to about 2.6. The WSi_(x) layer can be deposited on top of a layerof polycrystalline silicon, an SiO₂ layer, or directly on top of asemiconductor wafer, such as a silicon or gallium arsenide wafer.

The WSi_(x) film is deposited using chemical vapor deposition (CVD)processes. In a preferred two-stage CVD process, a substrate is placedin a deposition chamber having first and second gas inlets. A mixeddeposition gas is formed by combining a silicon source gas and atungsten source gas sufficiently upstream of the deposition chamber thatthe mixed deposition gas is substantially uniformly mixed prior tointroduction into the deposition chamber.

During an initial deposition stage of the process, the mixed depositiongas is introduced into the deposition chamber through the first gasinlet. Separately, a seeding gas is introduced into the depositionchamber through the second gas inlet. The deposition chamber ismaintained at process conditions suitable for depositing a WSi_(x)interfacial layer with a uniform Si:W ratio on the substrate.

During a second deposition stage of the process, the flow of seeding gasis stopped while continuing to introduce dichlorosilane and tungstenhexafluoride into the deposition chamber. The deposition chamber ismaintained at process conditions suitable for depositing a substantiallyuniform, substantially fluorine-free, WSi_(x) layer on the substrate.

Preferably, the silicon source gas and the tungsten source gas arecombined at least 2.5 inches upstream of the deposition chamber. Morepreferably, the silicon source gas and the tungsten source gas areselected so that there is substantially no gas phase nucleation of thegases when the gases are mixed.

DRAWINGS

These and other feature, aspects, and advantages of the presentinvention will become better understood with reference to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1a is a schematic view of a chemical vapor deposition apparatussuitable for preparing the WSi_(x) films of the present invention;

FIG. 1b is a schematic view of another version of the mixing assembly ofFIG. 1a;

FIG. 1c is a schematic view of another chemical vapor depositionapparatus suitable for preparing the WSi_(x) films of the presentinvention;

FIGS. 2 and 3 graphically present resistivity of various WSi_(x) films,varying with depth into the film;

FIGS. 4 and 5 present RBS spectrum of a WSi_(x) film with anunsatisfactory Si:W ratio in the interfacial region of the film, beforeand after annealing, respectively;

FIGS. 6 and 7 present RBS spectrum of a satisfactory WSi_(x) filmproduced by a process according to the present invention, before andafter annealing, respectively; and

FIG. 8 presents a SIMS spectrum for a WSi_(x) film produced by a processaccording to the present invention, showing the low fluorine impuritycontent in the film.

DESCRIPTION

The present invention is directed to WSi_(x) films with a value of xthat is substantially uniform through the thickness of the film, andwhich contain less than 10¹⁸ fluorine atoms/cc, and more preferably lessthan 10¹⁷ fluorine atoms/cc. By "substantially uniform" it is meant thatthe average value of x within each strata of the WSi_(x) layer isbetween ±10% of the average bulk value of x through the thickness of theWSi_(x) layer. Typically, the bulk value of x is from about 2.0 to about2.8, and preferably the value of x is from about 2.2 to about 2.6. Thesubstantially uniform WSi_(x) film is deposited on substrates usingchemical vapor deposition processes.

Substrates

The WSi_(x) film can be deposited on a wide variety of substratesincluding glasses, plastics, metals, and semiconducting waferscomprising silicon, silicon oxide, polysilicon and gallium arsenide.Moreover, the WSi_(x) layer can be deposited on top of other layers suchas a layer of Si₃ N₄, polysilicon, thermally oxidized SiO₂, or acombination of these layers. Also, additional layers can be deposited onthe WSi_(x) film.

Deposition Chamber

The chemical vapor deposition chamber used to deposit the substantiallyuniform WSi_(x) film is preferably conventional low pressure CVDequipment such as those sold by Applied Materials of Santa Clara,Calif., and described in T. E. Clark, et. al., Tungsten And OtherAdvanced Metals for VLSI/ULSI Applications V, Edited by S. S. Wong andS. Furukawa, (Mat. Res. Soc. Proc., Pittsburgh, Pa. 1990) page 167.

With reference to FIG. 1a, an apparatus 10 suitable for preparing filmsaccording to the present invention comprises a deposition chamber 12, anexhaust system 14, and a gas combining or mixing assembly 16. Asubstrate 20, such as a silicon based semiconductor wafer, horizontallyrests on top of a support or susceptor 24. A heater 26 lies directlybeneath the support 24 and is used to heat the substrate 20. Adeposition or reaction zone 28 lies directly above the substrate 20.

The process gases used in the CVD process enter the deposition chamber12 through gas inlets 30, which lead into a "showerhead" type diffuser32. The diffuser 32 uniformly distributes the process gas in thedeposition zone 28. A gas combining or mixing assembly 16 can be used tomix or combine the deposition gases upstream of the showerhead 32, sothat the deposition gases are substantially uniformly mixed whenintroduced into the deposition zone 28.

The exhaust system 14 is connected to the chamber 12 through an exhaustline 40. The exhaust system 14 typically comprises a rotary vane vacuumpump (not shown) capable of achieving a minimum vacuum of about 10mTorr, and optionally can include scrubber systems for scrubbingby-product gases. The pressure in the chamber 12 is sensed at the sideof the substrate 20, and is controlled by adjusting a throttle valve 42in the exhaust line 40.

Process Gases

Preferably, the process gas comprises a deposition gas such as (i) asilicon source gas, such as dichlorosilane (DCS), and (ii) a tungstensource gas, such as tungsten hexa-fluoride (WF₆). Althoughdichlorosilane and tungsten hexa-fluoride are used to illustrate theinvention, any silicon or tungsten source gas, or combination of gases,known to those skilled in the art can also be used. Thus the scope ofthe inventions described herein should not be limited to use of DCS orWF₆.

A seeding or nucleation gas such as SiH₄ or H₂, can be added to theprocess gas to initiate deposition of a uniform layer of WSi_(x) on thesubstrate. The process gas can also contain a carrier gas, such as argonor helium.

The WF₆ and the DCS are transported through the feedlines 50 and 52,respectively. Mass flow controllers 54a and 54b and air operated valves56 are used to control the flow of the reactant gases into thedeposition chamber 12. The flow rates of the DCS and WF₆ affect the rateat which WSi_(x) film is deposited. A film deposition rate of at least100Å per minute provides a commercially feasible production rate.Preferably, a film deposition rate above about 500Å is obtained.

The volumetric flow ratio of DCS to WF₆ also determine the value of x inthe deposited WSi_(x) film. As the DCS to WF₆ ratio increases, theamount of silicon in the WSi_(x) layer, i.e., the value of x increases.The desired value of x (from about 2.0 to about 2.8), and the desireddeposition rates can be achieved by introducing DCS into the chamber ata volumetric flow rate from about 100 to about 1000 sccm, and tungstenhexa-fluoride at a volumetric flow rate of from about 2.5 to about 20sccm. Generally, the flow ratio of DCS to WF₆ is from about 5:1 to about400:1. Optionally, argon can be added to the gas flow at a rate of fromabout 100 to about 1000 sccm.

Pre-Mixing

It is preferred to pre-mix or combine the dichlorosilane and tungstenhexa-fluoride upstream of the deposition zone 28 as shown in FIGS. 1aand 1c. Combining the gases in a gas feedline upstream of the depositionchamber 12 results in a more uniform gas mixture being introduced intothe deposition zone 28. By "upstream" it is meant before, and at adistance from, the deposition chamber 12. Preferably, the gases arecombined in a feedline which is at least 2.5 inches (6.35 cms) upstreamof the deposition chamber 12. It is believed that upstream pre-mixingproduces a substantially more uniform initial gas mixture, therebyresulting in greater uniformity in the tungsten to silicon ratio in the"interfacial" layer of WSi_(x) film that is first deposited on thesubstrate.

A preferred method for combining the DCS and WF₆ upstream of thedeposition zone 28 utilizes a mixing/ non-mixing/diverting assembly 16,as shown in FIG. 1a. The assembly 16 allows switching between a gasmixing mode, a gas non-mixing mode, and a diverting mode. In the mixingmode, the apparatus 10 can be used for processes where the process gasesare mixed. In the non-mixing mode, the apparatus 10 can be used forprocesses where the process gases are not mixed. The assembly 16 alsoallows diverting of residual or contaminant process gases directly tothe exhaust system 14 in the diverting mode.

With reference to FIG. 1a, the assembly 16 comprises: (i) a valve 62 inthe WF₆ feedline 50, (ii) a valve 63 in the DCS feedline 52; (iii) afirst transfer line 64 with a pair of valves 66 therein, the line 64connecting the WF₆ feedline 50 to the DCS feedline 52; (iv) a secondtransfer line 70 with a pair of valves 72 therein, the line 70 alsoconnecting the WF₆ feedline 50 to the DCS feedline 52; and (v) amixing/diverting line 74 with a valve 76 therein, the line 74 connectingthe first transfer line 64, the second transfer line 70, and the exhaustline 40.

In order to mix or combine the process gases prior to their introductioninto the deposition chamber 12, the valves 62, 63, and 76 are "closed,"and both of the valves 66 as well as both of the valves 72 are "opened."This causes the WF₆ and DCS gases to be directed along arrows 84,thereby causing the WF6 to mix with the DCS in line 74. The pre-mixedprocess gases then re-enter the lines 50 and 52 through the open valves72a and 72b, and are introduced into the deposition chamber 12 throughthe gas inlets 30.

In the non-mixing mode, both of the valves 66 and both of the valves 72are closed, and the valves 62 and 63 are opened. This causes the WF₆ andDCS, to separately flow along the pipelines 50 and 52, respectively.

In the diverting mode, both of the valves 66 and the valve 76 areopened, and the valves 62, 63 and both of the valves 72 are closed. Thiscauses the process gases to be diverted directly to the exhaust line 40through the diverting line 74. The diverting mode is used at thebeginning of the process to divert residual process gases which remainin the feedlines 50 and 52, in order to stabilize the composition of theprocess gases in the feedlines 50 and 52, before pre-mixing andintroducing the process gases into the deposition chamber 12.

Another version of the assembly 16 is shown in FIG. 1b. This versiondoes not have a diverting line and has fewer valves. To mix the gases,the valves 62 and 72 are closed, and the valve 66 is opened. This causesthe WF₆ gas to be redirected into line 50, where the gas mixes with theDCS before being introduced into the deposition chamber 12.

Instead of using the assembly 16, it is also possible to combine thegases, by merging the pipelines 50 and 52 into a single pipelineupstream of the deposition chamber 12. Alternatively, it is alsopossible to mix the process gas in a mixing container.

Seeding Gas Process

A "seeding" or nucleation gas can be used to initiate deposition of anuniform interfacial WSi_(x) layer on the substrate. In this process, aseeding gas such as monosilane, disilane, trisilane or H₂ is added tothe process gas during the initial deposition stages for initiatingdeposition of an interfacial layer having a uniform Si:W ratio. Theseeding gas process is advantageous because it allows deposition of atungsten silicide film having a uniform sheet resistance, even for sheetresistivities greater than 1000 μΩ-cm. In tested examples, the variationin sheet resistance of tungsten silicide films deposited using a silaneseeding gas was lower than that obtained from prior art methods, thenon-uniformity in sheet resistance typically ranging from about 0.9 toabout 2%.

Preferably, the seeding gas is introduced into the deposition chambervia a separate gas inlet than the gas inlet used to introduce thedeposition gas. This prevents the seeding gas and deposition gases fromreacting to form contaminant particulates in the gas feedlines, via gasphase nucleation mechanisms. In this process, because the deposition gasis premixed, the silicon and tungsten source deposition gases areselected so that when the gases are mixed, substantially no gas phasenucleation occurs in the mixture of gases. Suitable deposition sourcegases for mixing at room temperature include dichlorosilane and WF₆.

A preferred mixing apparatus 10 allowing separate introduction of theseeding gas and the premixed deposition gas, is shown in FIG. 1c. Inthis apparatus 10, the silicon source gas and the tungsten source gasare combined upstream from the deposition zone 28 using a deposition gasmixing/diverting assembly 80, also known as a mixing manifold. Themixing assembly 80 combines the silicon source gas and the tungstensource gas at least 2.5 inches upstream of the deposition chamber 12.The mixing assembly 80 also allows switching between a deposition gasmixing mode, a cleaning gas mode, and a diverting mode. In the mixingmode, the apparatus 10 is used for deposition processes where thedeposition gases are mixed prior to introduction into the chamber 12. Inthe cleaning gas mode, cleaning gas, such as NF₃ is introduced into theapparatus 10 to clean the apparatus. The diverting mode allows divertingof residual or contaminant process gases directly to the exhaust system14.

With reference to FIG. 1c, the assembly 80 comprises: (i) a valve 82 inthe tungsten source gas (WF₆) feedline 84, (ii) a valve 86 in thesilicon source gas (DCS) feedline 88; (iii) a first transfer line 90with a pair of valves 92a, 92b, connecting the WF₆ feedline and the DCSfeedline to the first gas inlet 93 in the chamber 12; and (iv) amixing/diverting line 94 with a valve 96 therein, connecting the firsttransfer line 90 to the exhaust line 40. Typically, the mixing assembly80 is maintained at room temperature; however, the mixing assembly canalso be maintained at a temperature at which substantially no gas phasenucleation occurs during mixing of the deposition gases, usingconventional cooling means such as a refrigeration unit, or conventionalheating means such as electrical heating tape wrapped around thefeedlines.

A separate seeding gas assembly 98 allows separate introduction of theseeding gas into the chamber 12. A second feedline 100 with a pair ofvalves 100a, 100b therein, connects a seeding gas source and an argonsource to a second gas inlet 102 of the deposition chamber 12. Applicanthas discovered that separate introduction of the deposition and seedinggases prevents gas phase nucleation of the gases in the feedlines, whichcan form contaminant particulates which are difficult to clean.

To perform the two-stage seeding gas process, a substrate 20 istransferred to the deposition chamber 12, and heated to the processtemperature. Thereafter, the chamber 12 is alternately purged and pumpeddown using argon gas at a flow rate of about 300 sccm for at least about20 seconds. Thereafter, to obtain a uniform mixture of deposition gasesin the mixing assembly 80, initially the valve 93 is "closed" and thediverting valve 96 is "open" causing residual WF₆ and DCS gases to bediverted to the exhaust 14 until the gases are uniform in composition.The diverting mode is used at the beginning of the process to divertresidual process gases which remain in the feedlines, in order tostabilize the composition of the process gases in the feedlines, beforeintroducing the pre-mixed process gases into the deposition chamber 12.Thereafter, the valve 96 is shut and valve 93 is opened to allow theuniformly mixed deposition gases to flow through the first inlet 93.Typically, the mixed deposition gases are diverted for about 2 to 10seconds, more typically for 3 to 7 seconds, and most typically about 5seconds.

In the initial deposition stage of this process, the premixed depositiongases are introduced into the deposition chamber 12 through the firstgas inlet 93. Typically, the DCS is flowed at a volumetric flow ratefrom about 100 to about 1000 sccm, and the WF₆ is flowed at a volumetricflow rate of from about 1 to about 20 sccm. When DCS and WF₆ are used,the flow ratio of DCS to WF₆ is typically from about 5:1 to about 400:1.Optionally, argon can be added to the gas flow at a rate of from about100 to about 1000 sccm.

During the initial deposition stage, the seeding gas is separatelyintroduced into the deposition chamber through the second gas inlet 102.The seeding gas is typically flowed at a rate of about 10 to about 500sccm, and is preferably flowed at a rate of about 100 to about 400 sccm,for a period sufficiently long that the total volume of seeding gasintroduced into the deposition chamber ranges from about 1 scc to about125 scc. Typically, the seeding gas is introduced for a period rangingfrom about 1 to about 60 seconds, and more preferably from about 2 toabout 30 seconds. Most preferably, the seeding gas is introduced in thedeposition chamber 12 for less than about 20 seconds, or less than about10 seconds.

Further, in the initial stages, the deposition chamber 12 is maintainedat process conditions suitable for depositing a WSi_(x) interfaciallayer with a uniform Si:W ratio on the substrate, suitable temperaturesbeing described below. During introduction of the seeding gas, thepressure in the chamber is preferably maintained at about 1 to 10 Torr,more preferably from 1 to 5 Torr, and most preferably about 3 Torr.

In the second stage of the process, the flow of seeding gas is shut off,and only dichlorosilane and tungsten hexa-fluoride are flowed into thedeposition chamber, at the same flow rates or flow ratios describedabove. In this stage, the deposition chamber 12 is maintained at processconditions suitable for depositing a substantially uniform,substantially fluorine-free, WSi_(x) layer on the substrate, suitabletemperatures and pressures being described below.

Temperature The higher the temperature in the deposition zone 28, thehigher the deposition rate on the substrate 20. The minimum support 24temperature allowing commercially feasible deposition rates on thesubstrate 20 is about 430° C. Lower support temperatures result in ratesthat are too slow for commercially feasible products. The maximumtemperature is determined by the maximum use temperature of the CVDequipment. It has been discovered that support temperatures in excess ofabout 450° C. are preferred, temperatures between about 500° C. andabout 700° C. more preferred, and temperatures of about 550 to 625° C.most preferred.

The temperature of the substrate 20 referred to herein is thetemperature of the support 24, which is measured with a thermocouple,since it is impractical to measure the temperature of the substrate 20itself. Accordingly, all temperatures referred to herein aretemperatures at which the support 24 is maintained. Typically, thetemperature of the support 24 is about 20° C. to about 100° C. higherthan the temperature of the substrate 20. For example, when the supportis maintained at a temperature of 500° C., the substrate 20 is at atemperature of about 480 to 490° C.

The deposition chamber 12 can be heated using the radiation heatinglamps 26 beneath the support 24. Other conventional heating apparatuscan be used.

Pressure

The pressure in the deposition chamber 12 is maintained at at least 0.5Torr and preferably from about 1 Torr to about 20 Torr. If the pressureis over 20 Torr, delamination between the WSi_(x) film and theunderlying substrate can occur. If the pressure is less than about 0.5Torr, the same deficiencies as those observed in the prior art films,namely a non-uniform interface between the WSi_(x) film and thesubstrate 20, is observed.

A multiple-stage pressure process, typically a two-stage pressureprocess, or a single-stage pressure process can be used. These processesare described below.

Two-Stage Process

When the deposition chamber 12 contains impurities, such as residualsilicon containing deposits, it is preferred to use a two-stage process.The two-stage process comprises a high pressure first stage, followed bya low pressure second stage. It is believed that by operating initiallyat a higher pressure, the tendency of contamination to cause depositionof WSi_(x) strata with a silicon to tungsten ratio lower than desired isovercome. The process is not limited to use of two distinct pressures,but rather, multiple pressures can be used.

In the two-stage process, the first higher pressure is at least 1 Torr,to compensate for effects that tend to lower the Si/W ratio, and thesecond lower pressure is at least 0.5 Torr less than the first higherpressure, i.e., for a first higher pressure of 1 Torr, the lower secondpressure would be less than 0.5 Torr. Similarly, if the first higherpressure is about 2 Torr, the second pressure would be less than about1.5 Torr.

Generally, the first stage can last from about 10 seconds to about twominutes, and the second stage from about 30 seconds to about 5 minutes.The change in pressure from the first higher pressure to the secondlower pressure occurs over a finite period of time, i.e., the change ofpressure is not a step change.

The composition of the process gas can be changed during the depositionprocess. As the pressure is reduced, the reaction efficiency of DCSdecreases. This can require the flow ratio of DCS to WF₆ to beincreased. For example, when the first stage process is 10 Torr, theflow ratio of DCS to WF₆ would be about 25:1, and when the pressure isreduced to 1 Torr for the second stage, the ratio is about 37.5:1.However, it is not always necessary to change the flow ratio.

Preferably the temperature in the deposition chamber 12 is maintainedsubstantially the same during both stages, and preferably, in thetwo-stage process, the support 24 is heated to a temperature of about550° C.

Single-Stage Process

Rather than varying the pressure, it is also possible to obtain asubstantially uniform WSi_(x) layer by starting off with a cleaned andconditioned deposition chamber 12, and depositing the WSi_(x) layer in asingle-stage high pressure process, in which the chamber 12 ismaintained at a pressure of at least about 0.5 Torr, preferably at leastabout 1 Torr, and most preferably from about 1 Torr to about 20 Torr,and the support 24 maintained at a temperature of at least about 550° C.

To clean the chamber 12, NF₃ gas is introduced into the chamber 12, anda plasma generated. The plasma activated NF₃ reacts with siliconcontaining deposits in the chamber 12, such as deposits on the wall, toform gaseous silicon-fluoride compounds. The silicon-fluoride compoundsare removed from the chamber 12, thereby substantially cleansing thechamber 12 of silicon containing compounds. The plasma can be generatedwith RF energy and maintained at a power level of about 30 to 300 Watts,for about 10 to about 40 seconds per wafer processed in the chamber, toachieve adequate vaporization of the silicon containing compounds.

Any residual fluorine ions in the chamber 12 can be removed bypassivating the fluorine ions with a reactive hydrogen containing gassuch as hydrogen. Residual fluorine can be passivated by generating aplasma in the chamber which causes hydrogen ions from the reactivehydrogen containing gas, to react with substantially all of theunreacted residual fluorine atoms. Alternatively, monosilane can also beused to passivate the residual fluorine.

In the single-stage process, the first wafer produced immediately afterthe deposition zone 28 in the chamber 12 is conditioned, is usuallyunsatisfactory. The next twenty-five wafers produced are satisfactory.After processing of about twenty-five wafers, it is believed that thechamber 12 should be re-conditioned.

EXAMPLES

The following examples demonstrate the effectiveness of processesaccording to the present invention. In these examples, a single-waferprocess chamber, namely a "Precision 5000" low pressure CVD equipment assold by Applied Materials, Santa Clara, Calif., and described in Clark,et al., supra, was used to deposit WSi_(x) layer on a silicon wafer witha thermal oxide layer. The silicon wafer had a thickness of about 0.73mm and a diameter of either about 150 or about 200 mm, and was loadedusing a mechanical arm into the deposition chamber 12 from a load lockarea (not shown) maintained at a pressure of 7 Torr of nitrogen.

The wafer 20 was introduced into the deposition chamber 12 at roomtemperature, and placed on a radiatively heated support 24. The wafer 20typically equilibrated within 60 seconds and was at a temperature ofabout 20 to 100° C. lower than the support 24 temperature. When thewafer 20 achieved equilibrium temperature, the pressure in chamber 12was established using a flow of non-reactive gases through pipelines 50and 52, and the pressure controlled by the throttle valve 42 on theexhaust line 40. Process gases which include DCS and WF₆, were thenintroduced into the chamber 12 at the required flow rate through theshowerhead diffuser 32.

Annealing

After the WSi_(x) layer was deposited, in some tests, the wafer was thenannealed in flowing nitrogen at 900° C. for 30 minutes.

Characterization Procedure

The following techniques were used to characterize the WSi_(x) films:

(1) The compositional variation of the tungsten to silicon ratio throughthe thickness of the deposited WSi_(x) film was determined by RutherfordBackscatting Spectrometry (RBS) using a 2.275 Mev helium ion beam.

(2) The presence of impurities such as chlorine, fluorine, oxygen andcarbon in the deposited film was detected by secondary ion massspectrometry (SIMS), in a Cameca IMS4F system using a 14.5 KeV cesiumion beam. Ion implanted standards with known quantities of impuritieswere used to quantify the impurity levels in the SIMS profiles.

(3) The resistivity of the deposited film was measured on a "PROMETRIXRS-35" machine purchased from Prometrix, Santa Clara, Calif.

Examples 1-4 Multiple Stage Process

Examples 1-4 demonstrate that a two-stage pressure process, with a firsthigher pressure and a second lower pressure, produces substantiallyuniform WSi_(x) films with a Si:W ratio in the interfacial region of thefilm in the optimal range of 2.0 to 2.8.

Table I identifies the process conditions used at each stage of thetwo-stage processes of Examples 1-4. Examples 1-3 provided satisfactoryfilms and Example 4 provided an unsatisfactory film. In all theexamples, a silicon wafer with a thermal oxide layer was used for thesubstrate 20, and the gap between the showerhead 32 and the wafer 20 wasset at 0.45 inches. Examples 1 and 2 used a 150 mm diameter wafer, andExamples 3 and 4 used a 200 mm wafer.

The films of Examples 1 and 2, were processed using first higherpressures of 3 Torr and 5 Torr, respectively. FIG. 2 presents the linearresistivities of these films varying with depth into the film. Forcomparison purposes, FIG. 2 also presents the linear resistivity of abaseline film prepared by a single pressure process of 1.5 Torr and 550°C. for 80 seconds, using a WF₆ flow of 3.5 sccm, a DCS flow of 150 sccm,and an Argon flow of 500 sccm. It is seen from FIG. 2 that as theinitial or first higher pressure increases from 1.5 Torr (in the singlepressure baseline process) to 3 Torr (Example 1) and 5 Torr (Example 2),the resistivity of the interfacial regions of the films increases fromabout 400 μΩ-cm to about 1000 μΩ-cm. The higher resistivity indicatesthat the Si:W ratio in the interface is in the optimal range of fromabout 2.2:1 to about 2.6:1. Thus, a two-stage process with a firsthigher pressure and a second lower pressure, produces a WSi_(x) filmwith a desirable Si:W ratio.

The linear resistivity of the film of Example 3 is presented in FIG. 3.For comparison purposes, the resistivity of a baseline film prepared bya single pressure process of 1 Torr and 550° C. for 80 seconds, using aWF₆ flow of 3.5 sccm, a DCS flow of 150 sccm, and an Argon flow of 500sccm, is also presented in FIG. 3. The film of Example 3, processed at afirst higher pressure of 3 Torr, shows a resistivity of 1100 μΩn-cm atthe interfacial region, indicating that the Si:W ratio in the interfaceis above 2.0. In contrast the resistivity of the baseline film at 400μΩ-cm indicates an undesirable Si:W ratio at the interface, which wasdetermined by RBS spectroscopy to be about 1.8.

                                      TABLE I                                     __________________________________________________________________________            EXAMPLE 1                                                                              EXAMPLE 2                                                                              EXAMPLE 3                                                                              EXAMPLE 4                                          FIRST                                                                             SECOND                                                                             FIRST                                                                             SECOND                                                                             FIRST                                                                             SECOND                                                                             FIRST                                                                             SECOND                                         STAGE                                                                                 STAGE                                                                             STAGE                                                                             STAGE                                                                              STAGE                                                                            STAGE                                                                               STAGE                                                                             STAGE                               __________________________________________________________________________    TIME    20  60   20  60   20  60   30  90                                     (seconds)                                                                     PRESSURE                                                                                       1.5                                                                                    1.5                                                                                   1.0                                                                                     1.0                               (Torr)                                                                        WF.sub.6 (sccm)                                                                         3.5                                                                                  3.5                                                                                    3.5                                                                                   3.5                                                                                       3                               DCS FLOW                                                                                       150                                                                                    150                                                                                   150                                                                                     200                               (sccm)                                                                        ARGON (sccm)                                                                                   500                                                                                    500                                                                                   500                                                                                     500                               TEMPERATURE                                                                                    550                                                                                    550                                                                                   550                                                                                     510                               (° C.)                                                                 __________________________________________________________________________

The film of Example 4 provided unsatisfactory results indicating that atwo-stage process with a first higher pressure of 10 Torr and a secondlower pressure of 1 Torr is not suitable. The Si:W ratio in the film wasdetermined by RBS spectroscopy to be 5.4:1 in the first 1/6th of thefilm, 4:1 in the next 1/6th, and 2.6:1 in the last 2/3rds of the film.The high Si content in the interface was undesirable for the reasonsprovided above.

Examples 5-13: Single Stage Process

Table II presents the results of experiments which used a single-stagepressure process. These experiments reveal that substantially uniformand substantially fluorine-free WSi_(x) layers can be deposited onsubstrates by maintaining the chamber pressure at at least 0.5 Torr,preferably at least about 1 Torr, and by heating the support to atemperature of at least 550° C. It is preferred to clean the depositionchamber after the processing of every 25 or more wafers.

Examples 5-10 provided WSi_(x) films having satisfactory Si:W ratiosfrom about 2.0 to about 2.8. Comparison of the films of Example 6 and 7,and comparison of the films of Examples 8 and 9, show that increasingpressure reduces the variability of the Si:W ratio of the film. Example6 processed at 1 Torr shows a Si:W ratio of 2.41 to 2.48, while Example7 processed at a lower pressure of 0.5 Torr shows a larger Si:W ratiovariation of 2.2 to 2.55. Similarly, Example 9 run at a higher pressureof 1 Torr shows a lower Si:W ratio variation than Example 8 which wasrun at the lower pressure of 0.5 Torr.

                                      TABLE II                                    __________________________________________________________________________    Example No.                                                                            5    6    7    8    9    10   11   12   13                           __________________________________________________________________________    Support  550  600  600  600  550  550  510  510  510                          Temperature (° C.)                                                     Pressure (Torr)                                                                                  0.5                                                                              1      0.5                                                                               1                                                                                  0.5                                                                              1          10                        DCS (sccm)                                                                                     150150                                                                             150                                                                                150                                                                                 150                                                                              150                                                                                200                                                                                  200                                                                              200                        WF.sub.6 (sccm)                                                                            4                                                                                   4                                                                                  5                                                                                  4                                                                                      3                                                                                  3                                                                                       3                        Film Thickness (Å)                                                                 2250   1930                                                                               2770                                                                               2210                                                                                2600                                                                             1660                                                                               --       3180                                                                           --                          Annealed         yes  yes                                                                           no                                                                                  no                                                                                  no                                                                               no                                                                                 no                                                                                   no                                                                               yes                       Si:W ratio.sup.(1)                                                                         2.07-2.19                                                                        2.17-2.32                                                                          2.41-2.48                                                                          2.2-2.55                                                                            2.34-2.40                                                                        2.48-2.70                                                                          1.95-3.15                                                                         3.3-4.3                                                                             3.3-2.5.sup.(2)             Si:W ratio                                                                                    2.272.17                                                                           2.46                                                                               2.4                                                                                  2.36                                                                            2.59                                                                               --       --                                                                               --                        (average)                                                                     __________________________________________________________________________     .sup.(1) First number represents value for 1/3 of layer closest to the        interface, and the second number represents value for remainder of the        layer (except for Example 13 as noted below).                                 .sup.(2) Three different regions were present with the first 1/6 being at     3.3, a transition 1/6 at 4.7, and the remaining 2/3 at 2.5.              

Examples 11-13 provide results of unsatisfactory experiments run attemperatures of about 510° C. Examples 11 and 12 show that non-uniformSi:W ratios are obtained for films deposited at 510° C./1 Torr and 510°C./10 Torr, respectively. Example 12 shows that a pressure of 10 Torrincreases the value of x above the desirable range of 2.0 to 2.8.Example 13 shows the adverse effect of annealing Example 12. It isbelieved that the annealing step in Example 13 causes Si migrationresulting in a non-uniform WSi_(x) film.

FIGS. 4 and 5 show that annealing of an unsatisfactory WSi_(x) filmwhich has a Si:W ratio below 2.0 in the interfacial strata, results inmigration of silicon to the interface during the annealing process. Thesilicon migration is undesirable because it can result in the filmdelaminating from the substrate. The 2000 KeV peak in FIG. 4 shows thatthe interfacial region of the WSi_(x) film has a Si:W ratio of about1.5, i.e., below the desirable range of 2.0 to 2.8. FIG. 5 shows the RBSspectra of the same film, after the film was annealed in nitrogen at900° C. for 30 minutes. The 2000 KeV peak of FIG. 5 shows that the valueof x in the interface increased to about 3.3, indicating that siliconmigrated to the interface during the annealing step. It is believed thatthis high silicon ratio at the interface causes delamination of thefilm.

FIGS. 6 and 7 show that WSi_(x) films with interfacial Si:W ratios fromabout 2.0 to about 2.6, do not result in migration of silicon duringannealing. The 2000 KeV peak in FIG. 6, shows that the interfacialWSi_(x) layer has a value of x of about 2.5. FIG. 7 shows an RBSspectrum of the film of FIG. 6, after the film was annealed in nitrogenat 900° C. for 30 minutes. With reference to the peak between the pointsa and b in FIG. 7, the Si:W ratio at the interface of the WSi_(x) filmis about 2.2, and in the bulk of the film is about 2.3, indicating thatsilicon did not migrate to the interfacial region during annealing.Also, the value of x in the bulk of the film changes only about 0.1 fromthe value of x in the interface, indicating that the variability of xbetween the interfacial strata of the film and the bulk of the film isonly about +5%. Such a variability is preferred and does not causedelamination of the WSi_(x) layer.

FIG. 8 shows that a WSi_(x) film produced by a process of the presentinvention has an average fluorine content of about 7×10¹⁶ atoms/cc,i.e., less than about 10¹⁷ atoms/cc. The average bulk value of x in thisfilm was determined by RBS spectra to be about 2.5. This illustrates thelow fluorine impurity content of the WSi_(x) films of the presentinvention.

Example 14 Upstream Mixing

A uniform tungsten silicide film was deposited on the wafer 20 using thefollowing process conditions. The pressure was maintained at 5 Torr, andthe temperature of the substrate 20 maintained between 450-700° C. Theflow rate of WF₆ was 10 sccm, and the flow rate of SiH₂ Cl₂ was 500sccm.

The two gases were mixed in the mixing assembly 16 shown in FIG. 1b.This version of the assembly 16 did not include a diverting line. Theprocess gases were mixed by closing the valves 62 and 72, and openingthe valve 66. This caused the WF₆ to be redirected from feedline 50 intofeedline 52, thereby combining the two gases in the feedline 52. Thecombined gases entered the deposition chamber 12 though a single gasinlet 30, to deposit a uniform WSi_(x) film on the substrate.

The films and process of the present invention have significantadvantages. Because of the substantially constant Si:W ratios throughthe thickness of the films, and because of their low fluorine content,the films do not tend to delaminate from the underlying substrate. Thus,it is expected that fewer defective integrated circuits will be built,and the cost of integrated circuits will be lowered. Moreover, the filmscan be deposited using existing conventional equipment. Therefore,investments in expensive chemical vapor deposition equipment are notrequired.

Although the present invention has been described in considerable detailwith regard to the preferred versions thereof, other versions arepossible. For example, although a particular mixing gas assembly isshown, the apparatus can comprise other conventional mixing gasassemblies. Also, the process of pre-mixing the process gas upstream ofthe deposition chamber can be used with other CVD processes than thoseillustrated herein. Therefore, the appended claims should not be limitedto the descriptions of the preferred versions contained herein.

What is claimed:
 1. A chemical vapor deposition process for depositingWSi_(x) on a substrate, the process comprising the steps of:(a) placinga substrate in a deposition chamber having first and second gas inlets;(b) forming a mixed deposition gas by combining silicon source gas andtungsten source gas sufficiently upstream of the deposition chamber thatthe mixed deposition gas is substantially uniformly mixed prior tointroduction into the deposition chamber; (c) during an initialdeposition stage, introducing the mixed deposition gas into thedeposition chamber through the first gas inlet, separately introducing aseeding gas into the deposition chamber through the second gas inlet,and maintaining the deposition chamber at process conditions suitablefor depositing an interfacial layer on the substrate; and (d) during asecond deposition stage, stopping flow of seeding gas while continuingto introduce the mixed deposition gas into the deposition chamber, andmaintaining the deposition chamber at process conditions suitable fordepositing a WSi_(x) layer on the substrate.
 2. The process of claim 1,wherein in step (b) the silicon source gas and the tungsten source gasare combined at least 2.5 inches upstream of the deposition chamber. 3.The process of claim 1, wherein in step (b) the silicon source gas andthe tungsten source gas are selected so that substantially no gas phasenucleation of the gases occurs when the gases are mixed.
 4. The processof claim 1, wherein step (b) further comprises the step of maintainingthe mixed deposition gases at a temperature at which substantially nogas phase nucleation occurs in the mixed deposition gas.
 5. The processof claim 1, wherein the silicon source gas comprises dichlorosilane andthe tungsten source gas comprises WF₆.
 6. The process of claim 5,wherein during both stages of the process, the volumetric flow ratio ofdichlorosilane to WF₆ is from about 5:1 to about 400:1.
 7. The processof claim 1 wherein the seeding gas is selected from the group consistingof monosilane, disilane, trisilane and H₂.
 8. The process of claim 1wherein the initial deposition stage is performed for only a sufficientperiod to initiate deposition of an interfacial layer comprising WSi_(x)having a substantially uniform Si:W ratio.
 9. The process of claim 1wherein in step (c), the seeding gas is introduced in the depositionchamber for less than about 20 seconds.
 10. The process of claim 9wherein in step (c), the seeding gas is introduced in the depositionchamber for less than about 10 seconds.
 11. The process of claim 1wherein during both stages of the process, the substrate is heated to atemperature of at least about 450° C.
 12. The process of claim 1 whereinin step (c) the volumetric flow rate of the seeding gas ranges fromabout 10 to about 500 sccm.
 13. The process of claim 1 wherein in step(c) the total volume of seeding gas introduced into the depositionchamber during the initial deposition stage ranges from about 1 to about125 scc.
 14. A process for depositing a WSi_(x) layer on a substrate,the process comprising the steps:(a) placing a substrate within adeposition zone; (b) during an initial stage, introducing a firstprocess gas consisting of seeding gas into the deposition zone, andmaintaining the deposition zone at process conditions suitable fordepositing an interfacial layer on the substrate, the interfacial layercapable of serving as a seeding layer; and (c) during at least onesubsequent stage, flowing a second process gas comprising silicon sourcegas and tungsten source gas into the deposition zone, and maintainingthe deposition zone at process conditions suitable for depositing aWSi_(x) layer on the interfacial layer.
 15. The process of claim 14,wherein in step (b), the seeding gas consists of a silicon source gas.16. The process of claim 14, wherein in step (b), the seeding gas isselected from the group consisting of monosilane, disilane, trisilane,dichlorosilane, and H₂.
 17. The process of claim 14, wherein thesubstantially uniform WSi_(x) layer on the substrate is characterizedby: (i) is at least 300 Å thick, (ii) contains less than 10¹⁸ fluorineatoms/cc, (iii) comprises an average value of x within each strata ofthe WSi_(x) layer that is between ±10% of the average bulk value of xthrough the thickness of the WSi_(x) layer, and (iv) comprises a valueof x of from about 2.0 to 2.8.
 18. The process of claim 14, wherein instep (c) the silicon source gas and the tungsten source gas are combinedat least 2.5 inches upstream of the deposition chamber.
 19. The processof claim 14, wherein in step (c) the silicon source gas comprisesdichlorosilane and the tungsten source gas comprises WF₆.
 20. Theprocess of claim 19, wherein in step (c) the volumetric flow ratio ofdichlorosilane to WF₆ is from about 5:1 to about 400:1.
 21. The processof claim 14 wherein the seeding gas consists of monosilane.
 22. Theprocess of claim 14 wherein in step (b) the seeding gas is introducedinto the deposition zone only at the onset of the process and for asufficient period to deposit an interfacial WSi_(x) layer having asubstantially uniform Si:W ratio.
 23. The process of claim 22 whereinthe seeding gas is introduced in the deposition zone for less than about20 seconds.
 24. The process of claim 23 wherein the seeding gas isintroduced in the deposition zone for less than about 10 seconds. 25.The process of claim 14 wherein in step (b) the volumetric flow rate ofthe seeding gas ranges from about 10 to about 500 sccm.
 26. The processof claim 14 wherein in step (b) the total volume of seeding gasintroduced into the deposition zone during the initial deposition stageranges from about 1 to about 125 sccm.
 27. A process for depositing aWSi_(x) layer on a substrate, the process comprising the steps:(a)placing a substrate within a deposition zone; (b) during an initialstage, introducing a first process gas consisting of seeding gas intothe deposition zone, and maintaining the deposition zone at processconditions suitable for depositing an interfacial layer on thesubstrate, the interfacial layer capable of serving as a seeding layer;and (c) during at least one subsequent stage, flowing a second processgas comprising silicon source gas and tungsten source gas into thedeposition zone, and maintaining the deposition zone at processconditions suitable for depositing a WSi_(x) layer on the interfaciallayer, whereby the WSi_(x) layer is at least 300 Å thick, contains lessthan 10¹⁸ fluorine atoms/cc, comprises an average value of x within eachstrata of the WSi_(x) layer that is between ±10% of the average bulkvalue of x through the thickness of the WSi_(x) layer, and comprises avalue of x of from about 2.0 to about 2.8.
 28. The process of claim 27wherein the seeding gas comprises one or more of monosilane, disilane,trisilane, dichlorosilane, or H₂.
 29. The process of claim 27 whereinthe seeding gas consists of a silicon source gas.
 30. The process ofclaim 27 wherein the seeding gas consists of monosilane.
 31. The processof claim 27 wherein the silicon source gas and the tungsten source gasare combined at least 2.5 inches upstream of the deposition chamber. 32.The process of claim 27 wherein the silicon source gas comprisesdichlorosilane and the tungsten source gas comprises WF₆.
 33. Theprocess of claim 32 wherein the volumetric flow ratio of dichlorosilaneto WF₆ is from about 5:1 to about 400:1.
 34. The process of claim 27wherein the seeding gas is introduced into the deposition zone only atthe onset of the process and for a sufficient period to deposit aninterfacial layer comprising WSi_(x) having a substantially uniform Si:Wratio.
 35. The process of claim 27 wherein the seeding gas is introducedin the deposition zone for less than about 20 seconds.
 36. A process fordepositing a WSi_(x) layer on a substrate, the process comprising thesteps:(a) placing a substrate within a deposition zone; (b) during aninitial stage, introducing a first process gas consisting of seeding gasinto the deposition zone, and maintaining the deposition zone at processconditions suitable for depositing an interfacial layer on thesubstrate, the interfacial layer capable of serving as a seeding layer;and (c) during at least one subsequent stage, forming a second processgas by combining a silicon source gas and a tungsten source gas at least2.5 inches upstream of the deposition chamber, flowing the secondprocess gas into the deposition zone, and maintaining the depositionzone at process conditions suitable for depositing a WSi_(x) layer onthe interfacial layer.
 37. The process of claim 36 wherein the seedinggas consists of a silicon source gas.
 38. The process of claim 36wherein the seeding gas comprises one or more of monosilane, disilane,trisilane, dichlorosilane, or H₂.
 39. The process of claim 36 whereinthe silicon source gas comprises dichlorosilane and the tungsten sourcegas comprises WF₆.
 40. The process of claim 39 wherein the volumetricflow ratio of dichlorosilane to WF₆ is from about 5:1 to about 400:1.41. The process of claim 36 wherein the seeding gas consists ofmonosilane.
 42. The process of claim 36 wherein the seeding gas isintroduced into the deposition zone only at the onset of the process andfor a sufficient period to deposit an interfacial layer comprisingWSi_(x) having a substantially uniform Si:W ratio.
 43. The process ofclaim 36 wherein the seeding gas is introduced in the deposition zonefor less than about 20 seconds.
 44. A chemical vapor deposition processfor depositing WSi_(x) on a substrate, the process comprising the stepsof:(a) placing a substrate within a deposition zone; (b) forming aprocess gas by combining dicholorosilane and WF₆ in a feedline at leastabout 2.5 inches upstream from the deposition zone; (c) introducing theprocess gas into the deposition zone; (d) maintaining the pressure inthe deposition zone sufficiently low and heating the substrate to atemperature sufficiently high to deposit WSi_(x) on the substrate,wherein the process gas is combined sufficiently upstream of thedeposition zone so that the process gas is substantially uniform whenintroduced into the deposition zone, and whereby the uniform process gasdeposits a substantially uniform, substantially fluorine-free layer ofWSi_(x) on the substrate, the WSi_(x) layer having an average value of xwithin each strata of the WSi_(x) layer that is between ±10% of theaverage bulk value of x through the thickness of the WSi_(x) layer, thevalue of x being from about 2.0 to about 2.8.
 45. The process of claim44 wherein the process gas comprises a seeding gas for initiating thedeposition of WSi_(x) onto the substrate.
 46. The process of claim 44wherein the substrate is heated to a temperature of at least about 500°C.
 47. The process of claim 44, wherein the volumetric flow ratio of DCSto WF₆ is from about 5:1 to about 400:1.